S8) The HPA Axis & Growth Hormone Flashcards Preview

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Flashcards in S8) The HPA Axis & Growth Hormone Deck (28)
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1

Describe the relationship between the hypothalamus and the pituitary gland

The hypothalamus and pituitary gland form a complex functional unit that serves as the major link between the endocrine and nervous systems

2

Where is the pituitary gland found?

3

The hypothalamus and pituitary gland modulate a wide variety of processes.

Identify some

- Body growth 

- Reproduction

- Lactation

- Thyroid & adrenal gland function

- Water homeostasis

4

The pituitary gland consists of two distinct parts. 

What are they?

5

The anterior and posterior pituitary glands have distinct embryological origins.

Describe these

- Anterior pituitary gland (adenohypophysis) arises from evagination of oral ectoderm (primitive gut tissue)

- Posterior pituitary gland (neurohypophysis) originates from neuroectoderm (primitive brain tissue)

6

The hormones produced by nerve cells in the hypothalamus act via two distinct neurocrine pathways.

Describe these pathways

- Direct effects on distant target tissues via oxytocin and antidiuretic hormone from the posterior pituitary

- Hormones secreted exclusively into hypophyseal portal system affect endocrine cells within the anterior pituitary 

7

In 3 steps, outline the neuroendocrine function of the posterior pituitary gland

⇒ Oxytocin and ADH are produced by neurosecretory cells in the supraoptic and paraventricular nuclei of hypothalamus

⇒ Transported down nerve cell axons to the posterior pituitary

⇒ Stored and released from posterior pituitary into the general circulation

8

In four steps, describe the synthesis, transport, release and action of the hormones acting on the anterior pituitary gland

⇒ Hormones synthesised in hypothalamus

⇒ Hormones transported down axons and stored in median eminence

⇒ Hormones released into hypophyseal portal system

⇒ Hormones stimulate/inhibit target endocrine cells in the anterior pituitary gland

9

Describe the action of the hormones produced by the anterior pituitary gland

⇒ Endocrine cells of anterior pituitary secrete a variety of hormones into the bloodstream to act on distant target cells (endocrine function)

⇒ Anterior pituitary hormones also effect neighbouring cells (autocrine and paracrine function)

10

Which hormones are released from the posterior pituitary gland and what do they do?

- Oxytocin – milk let down and uterine contractions during birth

- Antidiuretic hormone – regulation of body water volume

11

6 tropic hormones produced in the hypothalamus and have direct effects on the release of anterior pituitary hormones.

Identify them

TRH – Thyrotropin releasing hormone / PRH

- PIH – Prolactin release-inhibiting hormone (dopamine)

- CRH – Corticotropin releasing hormone

- GnRH – Gonadotropin releasing hormone

- GHRH – Growth hormone releasing hormone

- GHIH – Growth hormone-inhibiting hormone (somatostatin)

12

Identify the 6 hormones produced in the anterior pituitary gland

TSH – Thyroid stimulating hormone

- ACTH – Adrenocorticotropic hormone

- LH – Luteinising hormone

- FSH – Follicle stimulating hormone

- PRL – Prolactin

- GH – Growth hormone

13

Summarise the relationship between the tropic hormones of the hypothalamus and the hormones produced by the adenohypophysis as well as their respective effects

14

Outline the hypothalamic-pituitary-adrenal axis as an example of a negative feedback system

15

Growth is influenced by many factors.

Identify some of these

16

Growth hormone is produced in the anterior pituitary.

Describe its stimulation and inhibition

Stimulation: hypothalamic GHRH

- Inhibition: hypothalamic Somatostatin 

17

How do growth hormones exert their effects?

- Growth-promoting effects mainly exerted indirectly via insulin-like growth factors (somatomedins)

- In response to GH cells of the liver and skeletal muscle produce and secrete IGFs 

18

Explain the role of GH and IGFs in bone development in childhood/teenage years as well as in adulthood

- In childhood/teenage years:

I. GH stimulates long bone growth length & width prior to epiphyseal closure (width after epiphyseal closure)

II. IGFs stimulate both bone and cartilage growth

- In adults:

I. GH & IGFs maintain muscle and bone mass and promote healing and tissue repair

II. GH & IGFs modulate metabolism and body composition

19

CNS regulates GH secretion via inputs into the hypothalamus affecting GHRH and somatostatin levels.

Describe some of these

- Deep sleep = surge in GH secretion

- REM sleep = ↓ GH secretion

- Exercise/stress = ↑ GH secretion

- Decreased glucose/FA = ↑ GH secretion

- Fasting = ↑ GH secretion

- Obesity = ↓ GH secretion

20

GH secretion is regulated by long loop and short loop negative feedback.

Describe the long loop negative feedback mechanism

Mediated by IGFs:

- Inhibit release of GHRH from hypothalamus

- Stimulate release of somatostatin from hypothalamus

- Inhibit release of GH from anterior pituitary 

21

GH secretion is regulated by long loop and short loop negative feedback.

Describe the short loop negative feedback mechanism

Short loop negative feedback – mediated by GH itself via stimulation of somatostatin release

22

What is the consequence of  growth hormone deficiency in childhood?

Pituitary dwarfism – proportionate type of dwarfism due to complete/partial deficiency 

23

What are the consequences of growth hormone excess?

- In childhood – gigantism (rare, often caused by pituitary adenoma)

- In adulthood – acromegaly (large hands, feet, lower jaw)

24

How does GH exert its effects on cells?

GH receptors activate Janus kinases (JAKs) 

25

There are 2 IGFs in mammals.

Describe their respective actions

- IGF1 – major growth factor in adults 

IGF2 – mainly involved in fetal growth

26

Binding proteins modulate the availability of IGFs.

What are the three ways in which IGFs communicate?

- Autocrine

- Paracrine

- Endocrine

27

IGFs act through IGF receptors (distinct from GH receptors) to modulate cell processes.

Identify four of these processes

- Hypertrophy

- Hyperplasia

- Increase in the rate of protein synthesis

- Increase in the rate of lipolysis in adipose tissue

28

Other hormones influence growth. Describe the growth-related actions of the following hormones:

- Insulin

- Thyroid hormones

- Androgens

- Oestrogens

- Glucocorticoids

Insulin – enhances somatic growth; interacts with IGF receptors

- Thyroid hormones – promote CNS development and enhance GH secretion

- Androgens – accelerate pubertal growth spurt; increase muscle mass; promote closure of epiphyseal plates

- Oestrogens – decrease somatic growth; promote closure of epiphyseal plate

- Glucocorticoids – inhibit somatic growth